Unstable angina is a syndrome which comprises a spectrum of symptomatic manifestations of coronary artery disease which lies between stable angina pectoris and acute myocardial infarction. Patients fall into three groups: angina of recent onset (4 weeks), angina of changing pattern, and angina occurring at rest (longer than 15 minutes). The syndrome may presage acute myocardial infarction or sudden death, or may itself be the manifestation of a myocardial infarction. The pathophysiology may involve primary cardiac events or extracardiac precipitating factors, and does not appear to be the consequence of a particular anatomic pattern of coronary artery disease. Pain may occur as a result of regional reduction of coronary flow to pressure-dependent areas of myocardium during states of increased myocardial oxygen demand. Persisting ischemia leads to infarction via a series of events which may include myocardial edema formation, increased beta-sympathetic tone, and others which have been experimentally modified by interventions designed to limit infarct size. Although the incidence of acute myocardial infarction and death was high in early studies, in recent reports acute infarction occurs in under 15.5 per cent and death in under 2 per cent. Patients at high risk are those pain persists with bed rest, and those with preceding stable angina pectoris or myocardial infarction. Prognostic differences among Groups 1, 2, and 3 may exist but cannot be assessed from available studies. Studies of the management of unstable angina have generally been uncontrolled. Hospitalization, bed rest, and short- and long-acting nitrates are generally employed in Groups 2 and 3 patients and the marked reduction in myocardial infarction rates from early to recent studies tends to support these approaches. Anticoagulants are less used now than formerly. Propranolol can produce a significant reduction of myocardial oxygen consumption and may redirect coronary flow to ischemic areas. The drug has effectively controlled pain in several studies and is now widely used to manage unstable angina. Aortocoronary bypass surgery has been extensively employed but there is only one preliminary report of a controlled study available. The role of surgery is not yet defined. The optimal approach to therapy may eventually involve the use of medical therapy, including beta-blockade to stabilize patients, with delayed semielective coronary angiography and surgery in those who respond. Emergency angiography and surgery might then be reserved for the high-risk group of patients whose pain persists during optimal medical therapy.